Abstract
An excess of in 2.4– year old ferromanganese crust (237KD) from the deep Pacific Ocean has been considered as evidence for the delivery of debris from a nearby supernova explosion to Earth. Extremely high (up to ) and concentrations (up to ) measured in 237KD cannot be supernova-derived. The helium is produced by galactic cosmic rays (GCR) and delivered in micrometeorites that have survived atmospheric entry to be trapped by the crust. is produced by GCR reactions on Ni in extraterrestrial material. The maximum of 237KD (80–850) is comparable to the GCR production ratio (400–500) predicted for Ni-bearing minerals in iron meteorites. The excess can be plausibly explained by the presence of micrometeorites trapped by the crust, rather than injection from a supernova source.
- Received 6 October 2006
DOI:https://doi.org/10.1103/PhysRevLett.98.141103
©2007 American Physical Society